New challenges face South Dakota with zebra mussels on the move

Infestation of Lake Sharpe, fears about Francis Case and Oahe has GF&P upping its response.

Written By:
Marcus Traxler / Forum News Service |
Oct 2nd 2019 - 8pm.

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A handful of zebra mussels are pictured at the Midway dock along Lewis and Clark Lake in October 2015. (Sam Stukel / S.D. Dept. of Game, Fish and Parks)

PIERRE, S.D. — Zebra mussels have South Dakota’s leaders’ attention. And they’re coming up with a plan to play defense.

The South Dakota Department of Game, Fish and Parks recently held a set of meetings in Oacoma and in Pierre regarding the discovery of the invasive species in Lake Sharpe and the concern about their potential spread to other nearby Missouri River reservoirs, including Lake Francis Case and Lake Oahe.

Mike Greiner, GF&P’s aquatic invasive species coordinator, said the state is continuing to put a high level of attention on the problems that zebra mussels can cause.

On Thursday and Friday, Oct. 3 and 4, the GF&P Commission is likely to approve adding both Lake Sharpe and Lake Francis Case to the list of designated containment waters for managing AIS in South Dakota. State officials believe there is a high probability that zebra mussels are in Lake Francis Case, as well, but that has not been confirmed.

In the meeting, Greiner pointed out that zebra mussels — which multiply at a rate that makes them nearly impossible to eradicate — are perhaps the biggest threat to public infrastructure, such as irrigators and water and power systems, and far more likely than wiping out a population of fish. Zebra mussels are about the size of a fingernail, and can attach to both sand surfaces and hard surfaces such as boats, docks, and anchors, and can block water intakes and hydroelectric equipment. They’ve also shown an ability to survive out of water for 30 days and with below freezing temperatures.

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“We know the impacts are more than just fishermen and recreational boaters. We are looking and trying to find partners for this work, especially with the funding,” Greiner said this week. “When the greatest impact is to infrastructure, the rhetorical question is do you pass the buck to all anglers with a fee to fund it when it affects everyone? Serious discussions are taking place and we want to explore every option. But where it will come from is a big unknown at this point.”

That cost to fight zebra mussels and other invasive species is likely to be passed on to consumers, Greiner said, making it more than just an outdoor enthusiasts’ problem. For example, the Missouri River provides drinking water for more than 200,000 people.

“Anyone that turns on a light switch or drinks water is affected in the cost to mitigate these invasive species,” he said.

Zebra mussels have been in Lewis and Clark Lake since November 2014 and since 2016. There has been exponential growth in adult populations, and spreading upstream and downstream to all connected waters. Greiner said GF&P still hasn’t found that “tipping point” for the population, and the species is continuing to increase in abundance four years later.

On July 10, crews working on the Big Bend Dam at Fort Thompson found zebra mussels in Lake Sharpe on the Missouri River. The mussels have been discovered as far north as the West Bend State Recreation Area, which is northwest of Lower Brule.

Since the discovery on Lake Sharpe, GF&P officers and officials have stepped up the response. They’ve met with marina operators and boat repair shops, and increased messaging and marketing about zebra mussels being a risk in the area. Law enforcement increased its presence, conducting roving inspections and checking more than 800 boats and issuing 104 citations, while nearly 1,000 watercraft were inspected, as well.

“People are how they are moved around,” Greiner said. “Really, the personal actions of boaters and anglers will still go the longest way. More strict regulations and more inspections, those are actions we can take, but the most impact can be done by people taking personal responsibility.”

Considering changes

Sharpe, Francis Case and Oahe’s reservoirs pose a different challenge for GF&P officials than the Lewis and Clark Lake. Those reservoirs are popular with boaters and outdoor enthusiasts from throughout South Dakota, more so than Lewis and Clark. Heat maps created from summer GF&P surveys of boaters and fishermen showed that the draw from out-of-state boaters was also strong, with nearly 23 percent of the boats recorded coming from out of state at Sharpe, while more than 38 percent visited Francis Case. Nebraska, Iowa and Minnesota, in that order, were the three most popular states for out-of-state visitors to the Missouri River reservoirs in the center of the state.

“For Sharpe and Francis Case, and that goes for Oahe, you really get boaters from every corner of the state and from out of state, as well. You didn’t have that as much on Lewis and Clark,” Greiner said. “With that many more boat ramps and that many more routes of travel, it’s much more difficult to inspect every single boat, making sure people are following the rules and draining all of the water out of the boats.”

GF&P leaders have also been considering cost-effective ways to contain the aquatic invasive species and keep it from spreading. Because staffing every boat ramp in the Missouri River is not feasible — it was deemed to cost about $9 million per year — a focus is on critical control points leading away from the river on state highways.

One idea on the table, Greiner said, is setting up mandatory stations where boaters leaving the AIS-impacted areas would be required to stop, and hot water decontamination equipment would be available to kill and remove anything from those boats before they leave. Manning every boat ramp on the Missouri River reservoirs wouldn’t be feasible, so inspection stations would be a more cost-effective option on a smaller scale. Containment and inspection stations would be set up near key highways leaving the river, and at certain border entrances into the state.

One estimate is adding about 35 stations with about 140 seasonal employees at a cost of about $2.9 million annually. That would give South Dakota a mixture of prevention and containment opportunities, Greiner said, and would be a scaled-down version of what has been successful in the western United States.

Over the next year, Greiner said the plan is to work with other state agencies, such as the Departments of Agriculture, Environment and Natural Resources, Transportation and Tribal Relations to figure out how other organizations can help stop the spread of invasive species. GF&P will also search for what is the best way to assure there is consistent enforcement of the mussels rules, such as draining boats and taking plugs in and out as boats enter and exit the water, and requiring operators to inspect their boats when they leave the boat ramp. Greiner said changes in the state’s management of zebra mussels will take place before next season.

“What we’ve had in the last year has been a game-changer,” he said. “We know change is coming and we’re going to be working to get adjustments in place.”

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A handful of zebra mussels of various sizes are pictured next to a penny, as taken from Lewis and Clark Lake in August 2015. (Sam Stukel / S.D. Dept. of Game, Fish and Parks)

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A handful of zebra mussels are pictured at the Midway dock along Lewis and Clark Lake in October 2015. (Sam Stukel / S.D. Dept. of Game, Fish and Parks)